Energy audit found frost on rafters in the attic
We live in Minnesota. We recently had an energy audit. The inspector found frost on the rafters in one of the attics along with the plywood starting to separate. The house was reroofed in 2008 and I remember that they replaced quite a few sheets of plywood. There is some blown in insulation and batts. The bathroom vent is sealed and vented to the outside. We don't humidify the house other than a shower in the lowest level and cooking.
What would be the first thing to do to stop the frost and keep things warm in the house?